Method for preparing a fatty substance ester and use thereof in pharmaceutics, cosmetics or food industry.
The present invention relates to a novel process for the preparation of an ester of fatty substance and of an alcohol chosen from the group consisting of sterols, stanols, 4-methylsterols and their hydrogenated homologs, triterpene alcohols and their hydrogenated homologs, and the mixtures of these, this ester being intended in particular for a pharmaceutical use, in particular a dermatological use, and for a cosmetic or food use.
Phytosterols (family of the phytohormones) and essential fatty acids are compounds with a high biological activity which are therefore advantageous [lacuna] the fields of pharmaceuticals, cosmetics and the human diet.
Phytosterols are compounds of terpene origin which constitute the major fraction of plant unsaponifiable materials, an example of which is xcex2-sitosterol. Since the 50s, phytosterols have been known in particular for their hypocholesterolemic action (Ling and Jones (1995), Life Sciences, Vol. 57, No. 3, pp. 195-206). The hypothesized mechanism of action is as follows: phytosterols lead to a decrease in the blood cholesterol by competing with the latter for its dissolution within the micelles of the bile salts in the intestine. In addition, the sterols lead to a decrease in the blood cholesterol (LDL) and a slight increase in the synthesis and excretion of endogenous cholesterol.
In an analogous way, polyunsaturated fatty acids (PUFAs) play an essential role at the nutritional level. By way of example, linoleic acid is an essential compound to the body since the latter cannot synthesize it (Delplanque et al. (1999), Olxc3xa9agineux Corps Gras Lipides [Oleaginous Lipid Fatty, Substances], Vol. 1, pp. 86-93). It is in fact the starting member of the metabolic series of the n-6 or xcfx89-6 PUFAs, fatty acids which are vital to the body. This series of acids comprises in particular arachidonic acid (C20:4), which is at the basis of the synthesis of chemical mediators, such as eicosanoids, which control numerous functions of the body, in particular platelet aggregation, the renal function and the immune response. Mention may also be made, among essential fatty acids, of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), for their preventive role with respect to cardiovascular diseases and some cancers.
Finally, at the dermocosmetic level, sterols and essential fatty acids are also essential compounds. Sterols are known for their antiinflammatory and antierythematous properties, in addition to their soothing and restructuring action (Wachter, Salka, Magnet, Cosmetics and Toiletries, (1995), Vol. 110, pp. 72-80). Furthermore, by limiting transepidermal water losses, mono- and polyunsaturated fatty acids for their part have a moisturizing and nutritional action. Finally, sterols and PUFAs have an important role in the synthesis of the lipids of the epidermal cutaneous barrier.
With the aim of increasing the bioavailability of sterols, and of stanols, their saturated homologs, it is known in the prior art to increase the lipophilicity of these compounds by subjecting them to an esterification reaction with a fatty substance, in particular a fatty acid or a derivative of the latter, preferably in the presence of a catalyst.
Currently, sterols and stanols are esterified by a transesterification reaction in the presence of homogeneous basic catalysts, such as sodium methoxide. The presence of NaOMe necessitates additional stages in which the catalyst in destroyed, leading to the formation of salts which it is absolutely essential to destroy. All these latter operations represent a very high additional coat in the production of these esters of sterols and of stanols. Furthermore, the use of homogeneous catalysts can promote side reactions in which the compounds are decomposed, the effect of which may be to modify the final appearance of the product (color and/or smell).
Heterogeneous catalysis, in comparison with homogeneous catalysis, exhibits the advantage of employing catalysts which can be more easily separated from the reaction medium and of creating fewer problems of corrosion and of side reactions. Mention may thus be made of magnesium oxide, which, however, exhibits the disadvantage of causing dehydration side reactions and/or reactions in which unsaturated bonds are isomerized, which reactions are unacceptable, in particular in the case of products intended for food use.
It has now been found, entirely surprisingly and unexpectedly, that the use of a certain class of compounds makes it possible to obtain an excellent heterogeneous catalysis effect for the esterification reaction involving at least one fatty substance and at least one sterol and/or one stanol and/or one 4-methylsterol, or a hydrogenated homolog of the latter, and/or one triterpene alcohol, or a hydrogenated homolog of the latter. The fatty substance esters obtained by the process according to the invention are very particularly suitable for the sectors of pharmaceuticals, in particular dermatology, cosmetics and specialized food (functional foods, medicinal foods, cosmetic foods).
The present invention thus relates to a process for the preparation of a fatty substance ester, characterized in that at least one fatty substance is subjected to an esterification reaction with at least one alcohol compound chosen from the group consisting of sterols, stanols, 4-methylsterols and their hydrogenated homologs, triterpene alcohols and their hydrogenated homologs, and mixtures of these, in the presence of at least one solid catalyst chosen from the group consisting of oxides of lanthanide metals and mixtures of these oxides.
The term xe2x80x9csolid catalystxe2x80x9d is understood to mean, according to the invention, a catalyst which is undissolved in the remainder of the liquid reaction medium and which can be recycled after use.
The term xe2x80x9clanthanide oxidexe2x80x9d is understood to mean, according to the invention, an oxide chosen from the group consisting of lanthanum oxide, cerium oxides, praseodymium oxides, neodymium oxides, promethium oxides, samarium oxides, europium oxides, gadolinium oxides, terbium oxides, dysprosium oxides, holmium oxides, erbium oxides, thulium oxides, ytterbium oxides, lutenium oxides and mixtures of these oxides.
The solid catalyst is preferably chosen from the group consisting of lanthanum oxide La2O3, ceric oxide CeO2, praseodymium oxides PrO2, Pr6O11 and Pr2O3, samarium oxide Sm2O3 and mixtures of these oxides.
More particularly, the solid oxide is preferably lanthanum oxide La2O3.
The solid catalyst can be provided in particular in a solid form chosen from the group consisting of powders, grains (pellets), beads, extruded forms and mixtures of these.
Preferably, the solid catalyst is in the form of a powder having a mean particle size of in particular between 1 and approximately 1000 micrometers, more particularly between approximately 10 and approximately 500 micrometers and very particularly preferably between approximately 50 and approximately 100 micrometers.
The solid catalyst can be supported on an inert support, that is to say a support which is inert in the presence of the reactants and products of the esterification reaction, such as the porous or nonporous inert supports known to a person skilled in the art, for example alumina or silica.
The oxides of lanthanides used as catalysts in the process according to the invention can be prepared according to methods known to a person skilled in the art, including when a supported catalyst is involved. They are also commercially available, such as the xe2x80x9cLSAxe2x80x9d and xe2x80x9cHSAxe2x80x9d forms sold by Rhodia.
The weight of catalyst to be used in the process according to the invention can be determined by a person skilled in the art using his overall knowledge, in particular with regard to the esterification reaction.
In particular, the solid catalyst used in the process according to the invention is present in the reaction medium in a proportion of between approximately 0.01 and approximately 30% by weight and more particularly between 1 and 5% by weight, with respect to the total weight of the reaction medium.
The esterification reaction employed in the process according to the invention can be any esterification reaction in which one of the starting reactants is a sterol and/or a stanol and/or a 4-methylsterol, or a hydrogenated homolog of the latter, and/or a triterpene alcohol, or a hydrogenated homolog of the latter, such as the direct esterification reaction between these alcohol compounds and a carboxylic acid or its acid chloride or anhydride or alternatively the transesterification reaction by alcoholysis between these alcohol compounds and an ester.
The term xe2x80x9cfatty substancexe2x80x9d is understood to mean, according to the invention, in agreement with the overall knowledge of a person skilled in the art, a molecule comprising, first, at least one chemical functional group which can react with an alcohol compound in an esterification reaction as described above, in particular a carboxylic acid, acid chloride, acid anhydride or, in the case of a transesterification by alcoholysis, an ester functional group. Secondly, the molecule of the fatty substance comprises at least one xe2x80x9cfattyxe2x80x9d hydrocarbonaceous chain, that is to say a linear hydrocarbonaceous chain of at least 7 carbon atoms which is saturated or unsaturated and optionally substituted, in particular a linear C7-C30 hydrocarbonaceous chain. The fatty chain is preferably a linear, ethylenically unsaturated, C7-C30 hydrocarbonaceous chain comprising at least one ethylenic unsaturation. More particularly, the fatty chain is a linear, ethylenically unsaturated, C7-C30 hydrocarbonaceous chain comprising at least two conjugated or nonconjugated ethylenic unsaturations, such as, for example, in the case of methyl linoleate.
In particular, the fatty substance is chosen from the group consisting of saturated fatty acids, in particular capric acid, lauric acid, stearic acid, or also myristic acid, palmitic acid and mixtures of these, and unsaturated fatty acids, in particular undecylenic acid, oleic acid, ricinoleic acid, linoleic acid, or also xcfx89-3 acids, such as linolenic acid and those of formulae: 
Docosopentaenoic Acid (DPA, C22:5/n-3) and the mixtures of these.
Mention will also be made, among fatty acids which can be used as fatty substances for these esterification reactions, of in particular the fatty acids obtained from fatty acid soaps which are byproducts from the saponification of a vegetable oil or from the refining of oils (soap stocks). This is because this represents a very advantageous enhancement in value of these byproducts from the preparation of vegetable oil unsaponifiable materials.
Mention may in particular be made, among vegetable oils which can be used, of sunflower oil, palm oil, palm kernel oil, coconut oil, grape seed oil, black mustard oil, poppyseed oil, karite butter oil, sweet almond oil, soybean oil, avocado oil, lupin oil, groundnut oil, cottonseed oil, sesame oil, olive oil, corn oil, cocoa oil, castor oil, ben oil, linseed oil, rapeseed oil, annatto oil, wheat germ oil, safflower oil, walnut oil, hazelnut oil, rapeseed oil, rice bran oil and mixtures of these oils.
The saponification of the oil, in particular of avocado oil (or soybean oil), is an essential stage in the process for producing the unsaponifiable materials. This stage, carried out in the presence of aqueous potassium hydroxide and of ethanol, is a basic hydrolysis of the oil (triglycerides), resulting in the formation of potassium soaps and of glycerol: 
The unsaponifiable material, as an emulsion in the aqueous/alcoholic phase (xe2x80x9csoapyxe2x80x9d phase), is subsequently extracted with dichloroethane (DCE) according to a liquid-liquid extraction process.
After the stage of liquid-liquid extraction, the xe2x80x9csoapyxe2x80x9d phase is acidified with sulfuric acid. The soaps are then converted to fatty acids (reaction 1 below). The mixture obtained is subsequently distilled in order to remove the ethanol and the traces of DCE. The fatty acids and the water are finally separated by settling.
2 RCOOxe2x88x92K++H2SO4xe2x86x922 RCOOH+K2SO4xe2x80x83xe2x80x83(1)
These crude avocado fatty acids are finally purified, for example on a silica column (eluent: hexane then hexane/diethyl ether 95/5) or by molecular distillation, and can thus constitute the starting material used during the preparation of fatty esters of avocado and of sterol and/or of stanol [lacuna], or of a hydrogenated homolog of the latter, and/or of triterpene alcohol, or of a hydrogenated homolog of the latter, according to the process of the present invention.
Soybean fatty acids or fatty acids of another vegetable oil, such as those mentioned above, can be obtained according to the same synthetic group.
Thus, according to a specific embodiment, the fatty substance esterified according to the invention is a fatty acid from at least one hydrogenated or non-hydrogenated vegetable oil, it being understood that the expression xe2x80x9cvegetable oil fatty acidxe2x80x9d encompasses, according to the invention, the fatty acids originally present in said vegetable oil and the fatty acids which can be obtained by treatment of the soapy phase after saponification of said vegetable oil, as described above.
Finally, the fatty substance esterified according to the invention, in the case of an esterification by alcoholysis (transesterification), can be an ester of a fatty acid, such as the fatty acids described above, in particular an ester in which the alkyl part of the alkoxy group is a C1-C22 alkyl part, for example an ethylhexyl part, and more particularly a C1-C6 alkyl part, such as the methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, pentyl or hexyl group, and more particularly still a C1-C3 alkyl part.
Mention may in particular be made of methyl laurate, methyl myristate or also methyl oleate, methyl linoleate, methyl stearate, methyl undecylenate, butyl oleate, methyl ricinoleate, methyl palmitate or also methyl palmitoelate, and the mixtures of these.
Advantageously, the fatty substance esterified according to the invention can be in the form of at least one hydrogenated or nonhydrogenated vegetable oil comprising fatty acids and/or fatty acid esters, such as the vegetable oils already mentioned above, or a mixture of these hydrogenated or nonhydrogenated oils.
The alcohol compound used in the process according to the invention is chosen from the group consisting of sterols, stanols, 4-methylsterols and their hydrogenated homologs, triterpene alcohols and their hydrogenated homologs, and the mixtures of these.
The sterols and stanols used as starting material in the process according to the invention are compounds well known to a person skilled in the art.
The term xe2x80x9csterolxe2x80x9d is understood to mean more particularly, according to the invention, sterol, that is to say the compound perhydro-1,2-cyclopentano-phenanthrene having a hydroxyl group at the 3-position, and the sterol analogs of general formula (I) below.
The term xe2x80x9cstanolxe2x80x9d is understood to mean, according to the invention, the derivative hydrogenated at the 5-position of a given sterol as defined above.
Thus, preferably, the sterols and stanols which can be used as starting materials in the process according to the invention correspond to the following general formula: 
in which the unsaturation marked by a dotted line in the 5-position corresponds to the unsaturation in the case of sterols and R represents a saturated or unsaturated and linear or branched hydrocarbonaceous chain comprising from 1 to 25 carbon atoms. In particular, R is chosen from the group consisting of C1-C12 alkyl groups, C1-C8 alkoxy group, C2-C8 alkenyl groups, C2-C8 alkynyl group, C3-C8 cycloalkyl groups, halogenated C2-C8 alkenyl groups and halogenated C2-C8 alkynyl groups. The term xe2x80x9chalogenatedxe2x80x9d denotes one or more halogen substituent, namely one or more chlorine, fluorine, bromine or iodine atom(s).
Mention may in particular be made, among the sterols which can advantageously be used in the process according to the invention, of xcex2-sitosterol, xcex1-sitosterol, xcex3-sitosterol, stigmasterol or campesterol, and the mixtures of these. For example, xcex2-sitosterol can be used in the form of the product known as xe2x80x9cUltraxe2x80x9d (mainly comprising xcex2-sitosterol) as sold by Kaukas. In the case of use of a mixture of sterols, mention may be made, for example, of the product known as xe2x80x9cGenerolxe2x80x9d, mainly comprising xcex2-sitosterol (approximately 50% by weight), stigmasterol and campesterol, as sold by Henkel or the product xe2x80x9cPrimalxe2x80x9d from Kaukas.
Mention may in particular be made, among the stanols which can advantageously be used in the process according to the invention, of xcex2-sitostanol, stigmastanol or campestanol, and the mixtures of these. Of course, as is well known to a person skilled in the art, the stanols used in the process according to the invention can be obtained by catalytic hydrogenation of sterols, such as the abovementioned sterols, for example during a stage upstream of the esterification stage according to the invention, one using well-known catalysts, such as palladium, platinum, copper or nickel.
4-Methylsterols, as described in particular in the xe2x80x9cManuel des Corps Grasxe2x80x9d [Handbook of Fatty Substances], published by TecandDoc Lavoisier under the aegis of the Association Franxc3xa7aise pour l""Etude des Corps Gras [French Association for the Study of Fatty Substances] (1992 edition, Alain Karleskind and Jean-Pierre Wolff), have as biosynthetic origin cycloartenol and 24-methylenecycloartanol in plants and lanosterol in animals; they are characterized by the presence of a single methyl group in the 4a position, the other having been subjected to oxidative decomposition and removal in the form of carbon dioxide (Benveniste, 1986). The methyl group in the 14a position may either remain or be removed in the form of formic acid and replaced by a hydrogen atom. The cyclopropane ring in the 9-10-19 position may be maintained or else may be subjected to opening, giving rise to the 19 methyl group and to a double bond located in the 9(l1) or in the 8(9) position. The usual nomenclature uses the name of the related triterpene alcohol, preceded by xe2x80x9c3l-norxe2x80x9d; the systematic nomenclature is based on the name of the related sterol, preceded by xe2x80x9c4xcex1-methylxe2x80x9d.
The 4-methylsterols which can be used as alcohol compound in the process according to the invention are in particular those of following formula (II): 
in which the substituent Ch represents a group having one of the following formulae a to h: 
4-Methylsterols corresponding to this formula (II) and which can very particularly be used, alone or in the form of a mixture of the latter, as alcohol compound in the process according to the invention are mentioned in the following table 1.
The term xe2x80x9chydrogenated homologsxe2x80x9d of a 4-methylsterol is understood to mean, according to the invention, the corresponding 4-methylsterol compound or compounds in which the unsaturated bond or bonds which may be present have been hydrogenated (that is to say, converted to a saturated bond) according to methods well known to a person skilled in the art.
Mention may in particular be made among the triterpene alcohols which can advantageously be used in the process according to the invention, of xcex2-amyrin, erythrodiol, taraxasterol, cycloartenol, 24-methylene-cycloartanol, lanosterol and the mixtures or these.
The term xe2x80x9chydrogenated homologsxe2x80x9d of a triterpene alcohol is understood to mean, according to the invention, the corresponding triterpene alcohol compound or compounds in which the unsaturated bond or bonds which may be present have been hydrogenated (that is to say, converted to a saturated bond) according to methods well known to a person skilled in the art.
The molar ratios of the reactants for the process according to the invention are such that use is made in particular of a fatty substance:alcohol compound molar ratio of between approximately 0.5 and approximately 50 and more particularly between approximately 1 and approximately 2.
The temperature of the esterification reaction according to the invention is preferably between approximately 100 and approximately 400xc2x0 C. and more particularly between approximately 200 and approximately 250xc2x0 C. The pressure can be between approximately 0.05 and approximately 50 bar and more particularly between approximately 0.1 and approximately 5 bar. In order to avoid possible oxidation of the ethylenic bonds present, it is recommended either to purge the reaction medium and the reactants with an inert gas or to carry out the reaction under a stream of inert gas or a partial vacuum or to carry out the reaction under a pressure of inert gas of between approximately 0.1 and approximately 5 bar.
Although the process according to the invention can advantageously be carried out in the absence of solvent, it is possible, if appropriate, in particular when the alcohol is soluble with difficulty in the fatty substance, to use a solvent preferably chosen from the group consisting of alkanes, halogenated alkanes (in particular chlorinated alkanes), dimethylformamide (DMF) or dimethyl sulfoxide (DMSO).
By the process according to the invention, the esterification reaction results in the production of an ester exhibiting entirely acceptable organoleptic qualities (smell, color, taste), a low acid number and a minimal content of free alcohol.
Of course, the process according to the invention can additionally comprise the stages upstream or downstream of a catalyzed esterification reaction which are known to a person skilled in the art.
In particular, the purity of the product obtained can be further improved, for example by decoloration, deodorization or molecular distillation.
Furthermore, the use of solid lanthanide oxides as solid catalyst makes possible the use of an industrial process which is less damaging to the environment (saving of energy, recycling of the catalyst, byproducts and effluents and the complete absence of solvents), insofar as these oxides are particularly easy to recover and can be recycled, in comparison with the currently known catalysts for esterification of sterols, stanols, 4-methylsterols and triterpene alcohols, which require in particular their destruction with formation of salts.
Thus, by an appropriate choice of the pharmaceutical quality, in particular dermatological quality, cosmetic quality and/or food quality of the starting reactants, by using the overall knowledge of a person skilled in the art and by the improved separation of the catalyst from the reaction product at the end of the esterification, the process according to the invention makes it possible to obtain products which are particularly suited to use in the fields of pharmaceuticals, in particular dermatology, cosmetics and specialized food (functional foods, medicinal foods, cosmetic foods).
Thus, another subject matter of the present invention is the use of at least one fatty substance ester as obtained by the esterification process described above as pharmaceutically active agent, in particular dermatological agent, in a pharmaceutical composition, in particular a dermatological composition.
In addition, another subject matter of the present invention is the use of at least one fatty substance ester as obtained by the esterification process described above as cosmetically active agent in a cosmetic composition.
Finally, another subject matter of the present invention is the use of at least one fatty substance ester as obtained by the esterification process described above as food additive.
The following examples are intended to illustrate the present invention but should under no circumstances be interpreted as being able to restrict the scope thereof.